The present invention relates to a pipe coupling for driven-in pipes or the like equipped with coupling regions at respective free ends of the individual pipes, with the coupling regions being formed by a reduction in the wall thickness from the exterior of the end of one pipe at the coupling region and from the interior of the end of another pipe at the coupling region, the reduction extending along the one pipe for a predetermined length and along the other pipe a distance which generally corresponds to the predetermined length.
The repair of untight--and consequently polluting--fluid conduits, such as waste water channels and the like, has become increasingly significant in recent times. Various sanitation methods have been developed for such repairs, with the repair of installed conduits by use of relatively short pipes--called "short pipe relining" in the art--being of especial significance. With this method, the pipes are forced--by pressing or drawing--into the defective pipelines without excavation of the defective pipelines by entry through the control shafts of an existing pipeline system. Since, however, such control shafts have inner dimensions--through which the pipes must pass--which are limited in size, the maximum installed length of the individual pipes is correspondingly limited. Therefore, the pipes which are employed have a relatively short length of about one meter.
Different methods were developed in the past for the drawing or pressing of such insertable pipeline sections into defective pipelines. For example, one solution provides for the insertion of short sections of insertable pipe which have a selected outer diameter into a portion of an existing pipeline which has an internal diameter larger than the selected outer diameter of the pipes. The resulting constriction of the cross section of the pipeline which would occur at the location of the insertable pipe due to its smaller inner diameter is, however, not acceptable in many cases. Therefore, methods are preferred in which the existing inner cross section of the installed pipeline is maintained.
In these preferred methods, the defective portion of the pipeline is broken up using a hydraulicly or mechanically operated apparatus, and the resulting fragments of the defective portion of the pipeline are then pressed outwardly into the area surrounding the pipeline so as to form a tunnel where the defective portion of the pipeline had been. In this way, a short insertable pipe section of the same diameter as the defective pipeline can be pushed into the above-described resulting tunnel. In this case it is necessary for the exterior of the short insertable pipe section to be as smooth as possible since any projections which extend beyond the outer circumference of the short insertable pipe section would make pressing or drawing the short insertable pipeline sections more difficult or even impossible.
The technical periodical entitled "Abwassertechnik," Volume 5, 1987, pages 22-24, describes pipes for subterranean, controlled construction of non-enterable cross sections--DN 250 to DN 800--as well as individual coupling arrangements. These couplings can be stressed axially using pressure. These are complicated coupling techniques which--insofar as they relate to pipes made of polymer materials--must be produced with the use of additional, accessory parts, and additional work is required to conform these additional parts to their respectively required dimensions. Moreover, for the pipe couplings produced according to this reference to withstand the pressure stresses that will occur, thick wall cross-sections are required, particularly in the region of the coupling, which thereby precludes economical fabrication of such pipe couplings.
Pipes made of polymer materials are generally produced in a continuous extrusion process and, during a finishing process, these pipes are formed to precise exterior dimensions. Due to the cooling of such pipes, initiated by the finishing process, tensile stresses develop along the interior pipe surface in a circumferential direction which, depending on the manufacturing process and the thickness of the pipe wall, may be considerably large. The continuously extruded pipes, which in this example are cooled from the outside in, are cut into pipes having lengths appropriate for their intended use and are subjected to further, special dimensioning work. This dimensioning work resides in the working of the pipe ends, for example by reducing the outer diameter of the pipe wall at its end to form a male coupling end, and by enlarging the internal diameter of a pipe or coupling end of another pipe to form a female end to receive the male end.
The pipe wall cross sections resulting from the above-described dimensioning work have the form of steps at the respective free ends of the pipes which substantially coincide in length and thickness. The male and female ends can be formed as complementary or mirror-image offset coupling regions of the two pipes, and the dimensioning can be effected, for example, by machining. However, the reduction in cross section of these free pipe ends removes the circumferential forces which would otherwise stabilize the pipe wall at these locations, and consequently the existing internal stresses of the remaining portions of the pipe wall cause deformations of these pipe ends. These deformations are particularly significant for pipes composed of polymer materials, e.g. high-density polyethylene, which have a low modulus of elasticity. In this case, it may become impossible to produce a pipe coupling having true dimensions. As a result of the above-mentioned deformations, the individual pipes can only be connected with one another--if a connection is possible at all--in a manner which does not permit the realization of a permanent seal.
Amorphous polymer materials, such as, for example, PVC-U, can be made free of stresses by tempering them to closely below the Vicat softening point. However, the remaining wall cross section in the coupling regions would no longer be sufficiently strong to absorb the pressure and tensile forces occurring during installation or connection with another pipe to form a coupling.
The tempering process which can be used for the above-mentioned PVC-U material is not feasible for partially crystalline materials such as high-density polyethylene. For such materials, the stresses in the pipe wall can be reduced only by heating the pipe to near the crystallite melting range, which cannot be accomplished in practice without irreparable deformation of the pipe or of the pipe ends at the locations where such heating occurs.